The present invention relates in general to temperature sensors, and in particular to a new and useful apparatus and method of measuring temperature using time domain intensity transmission.
A number of methods may be used to measure temperature distribution throughout large area panels such as found, for example, in airplane wings. These methods include ultrasonic thermometry, optical time domain reflectometry, multiple point discrete sensing, and time domain intensity transmission, which is the subject of the present invention.
Ultrasonic thermometry is based on the measurement of changes in sound propagation through a material as a function of temperature. This technique was first applied at Babcock & Wilcox, a McDermott Company (B & W) about 30 years ago and technical refinements and extensions have continued to date. B & W has routinely applied ultrasonic thermometry to measure temperature distributions over large areas, in short time intervals, in support of thermal-hydraulic and heat transfer research programs.
Distributed temperature sensing based on optical time domain reflectometry takes advantage of temperature dependent losses in optical fibers. These losses may result, for example, from temperature dependent microbends along the fiber length. If a single fiber is interrogated by a short optical input pulse, the arrival time of reflected return pulses corresponds to specific positions along the fiber length. The magnitude of the reflected return pulses may be used to determine the magnitude of microbend loss and thus temperature at these specific positions.
Multiple point discrete temperature sensing is achieved by multiplexing onto a single light bus, the signals from optical fibers end-coated with silicon-film temperature sensors. B & W has demonstrated the critical technologies required to implement this technique originally demonstrated by others.
An article entitled "Self-referencing Multiplexing Technique for Fiber-Optic Intensity Sensors", by Spillman and Lord, J. of Lightwave Technology, Vol. LT-5, No 7, July 1987, discloses a sensor which can be used for sensing various parameters including temperature, which comprises a self-referencing sensor loop which receives a portion of light supplied from an optical source and recirculates it through a pair of couplers, to an output line connected to a photo detector. This reference does not disclose an array of fiber-optic power dividers as used in the present invention, with time delays for producing a time to space domain intensity separation.